When should I winterise my boat, and what conditions mean it is time?
I keep my boat afloat in a marina, but sometimes leave it for three or four weeks between trips. Should I winterise as soon as the nights turn cold, or can I wait until frost is forecast?
Answer
Winterise your boat after your last planned trip and before the first frost can reach its engine, plumbing or seacocks. If you keep boating through winter, service it now and provide reliable frost protection between trips, keeping the engine compartment above 0°C.
Check forecasts and visit dates
Base your timing on the lowest forecast temperature, how long the boat will be unattended and how reliably you can protect it. A fixed date tells you less: a sheltered coastal marina and an exposed inland boatyard can have very different conditions in the same week.
Start making arrangements when overnight temperatures regularly fall towards 5°C. This is a planning trigger, not the point at which water freezes. Finish frost protection before freezing conditions arrive. The first frost warning is too late to start booking an engineer.
- Freezing nights forecast before your next visit: protect the boat before leaving it.
- Several weeks without a planned trip: winterise while access and weather are still reasonable.
- Haul-out booked near the usual frost season: arrange engine and water-system protection alongside the lift.
- Unreliable shore power or frequent marina outages: do not depend on an electric heater as your only protection.
One brief frost does not automatically freeze an entire engine, but exposed pipes and small pockets of trapped water cool faster. Daytime temperatures cannot tell you whether every vulnerable component is safe.
Winter storage or regular use
If the boat will be unused, winterise the engine cooling system following the engine manufacturer's procedure. On a heat-exchanger-cooled inboard, this normally means protecting the raw-water circuit and checking the existing antifreeze in the separate closed coolant circuit. Raw-water-cooled engines need a different procedure. Identify your cooling arrangement first.
Change the engine oil and service the filters before storage. Contaminated oil left in the engine throughout winter encourages internal corrosion. Follow the service schedule for the correct oil grade and filter specification.
If you will use the boat regularly, keep the engine ready to run and maintain heat around it instead of repeatedly adding storage antifreeze. A thermostatically controlled frost guard can do this. A setting of around 5°C gives some margin above freezing; check the coldest part of the compartment with a minimum-temperature thermometer.
Use a heater suitable for unattended marine use. Secure it clear of combustible materials and supply it through a sound, RCD-protected electrical installation.
If heating the cabin, allow warmth into the engine space where the installation permits. A warm saloon does not prove that the engine compartment, cockpit locker or toilet inlet remains frost-free. Arrange checks and a response to power failure.